The overall objective of this proposal is to study the cause(s) of infertility observed in association with obesity. For this purpose the genetically obese female rat "Fatty" of the Zucker strain will be used as a model to study the ovarian, uterine and pituitary function. Unlike the obese mouse, the obese rat shows estrous cycles but fails to mate and the uteri do not form deciduomata in response to trauma during pseudopregnancy. Detailed studies of the endocrine and morphological changes during pseudopregnancy will be carried out in the obese rat and will be compared with lean litter mates. Response of the uteri to exogenous gonadal steroids will be studied at the macromolecular level. Attempts will be made to induce mating behavior by exogenous steroids. The characteristics of implantation will be studied by artificial insemination and ova transplants.